1. Field of the Invention
The present invention relates to a wind turbine blade, in particular, a partial pitch wind turbine blade having lightning conduction means.
2. Description of Related Art
Pitch systems are commonly used in wind turbine blades, to allow for the pitching of sections of a wind turbine blade relative to the airflow at the blade. They normally comprise hollow cylindrical structures having a first pitch section and a second pitch section, with a bearing runway or roll and a plurality of ball bearings provided within the runway located at the interface between the first and second sections. The bearings permit the first pitch section of the pitch system to rotate relative to the second pitch section.
With reference to FIG. 1, an enlarged section of a prior art partial pitch wind turbine blade is indicated generally at 10. The blade comprises a first blade section 12 and a second blade section 14, the first and second blade section 12,14 coupled together using pitch system 16 provided at the pitch junction of the blade 10, between the adjacent ends of the first and second blade sections 12,14. Accordingly, the second blade section 14 is operable to pitch relative to the first blade section 12, via the pitch system 16.
A partial pitch wind turbine blade comprising an inner blade extender section and an outer blade extender section where the outer blade extender section is coupled to the inner blade extender section by a pitch system such that the outer blade section is operable to pitch relative to the inner blade extender section which is know from European Patent Application Publication EP 2 031 245 A2.
As the pitch system is a vital component of the wind turbine architecture, it is standard procedure to protect the pitch system 16 from the damaging effects of a lightning strike on the wind turbine blades 10, often by positioning lightning receptors in the first and second blade sections 12, 14 to attract lightning strikes away from the pitch system.
Chinese Patent Application Publication No. 101793240 A discloses providing a lightning receptor on the exterior of the blade surface, with a lightning down conductor provided as a flexible wire which is routed through the interior of a pitch system provided at the root end of a blade, away from the pitch system bearings. Great care is taken to ensure that the lightning does not come into contact with the pitch system itself, by positioning the lightning down conductor such that it is spaced from the pitch system. The lightning down conductor can then be connected to the wind turbine tower or directly into the ground to dissipate the lightning strike.
The same teaching—ensuring that the lightning does not come into contact with a structural part of the blade—applies in European Patent Application Publication No. EP 2 243 955 A2 where fairings are applied to the wing and coupled to a grounding cable or lightning down conductor to protect or shield the metal joint of a two-section blade.
Further alterations provided for partial pitch rotor blades include positioning lightning receptors in the blade sections adjacent the pitch system and/or providing Faraday cages about the pitch system to protect the contained components, also while routing any lightning down connectors to avoid the pitch system itself. Such approaches result in additional steps during manufacturing of the wind turbine blades, resulting in increased costs, manufacturing effort, etc.